The present invention relates to a matrix display device having several sets of electrodes and to the process for controlling the same. It is used in opto-electronics and mainly in the control of the liquid crystal cells used more particularly as converters for converting electrical data into optical data, in the real time processing of optical images, in the production of colour filters which can be particularly used in colour television, and in analog display means.
More specifically, the invention relates to a matrix display device comprising a display cell constituted by two transparent insulating walls and by a material having a plurality of zones distributed in matrix-like manner and inserted between a first system of electrodes covering one of the two walls and defining p control columns and a second system of electrodes covering the other wall, constituted by parallel conductive strips and defining q control rows, the column x.sub.i in which i is an integer such that 1.ltoreq.i.ltoreq.p and row y.sub.j in which j is an integer such that 1.ltoreq.j.ltoreq.p defining an area x.sub.i y.sub.j of the material and comprising means making it possible to supply appropriate excitation signals to the rows and columns for exciting an optical property of the material.
Numerous devices of this type are known and use, for example, as the sensitive material a liquid crystal film and for which the excitation is of an electrical nature. Although the invention more particularly applies to such devices, it also applies in more general terms to any device comprising a material of which an optical property can be modified by means of a random excitation. This excitation can be of an electrical type, such as for liquid crystals, but also of a magnetic, thermal, electronic or other type. The material can be a solid, liquid, amorphous or crystalline body. The optical property can be an opacity, refractive index, transparency, absorption, diffusion, diffraction, convergence, rotary power, birefringence, reflected intensity in a given solid angle, etc.
In the case of a liquid crystal cell in which the excitation is of an electrical type, such known display devices are controlled by applying a periodic voltage V.sub.x of mean value zero to row x.sub.i and a zero voltage to the other rows, whilst applying to the columns y.sub.j periodic voltages V.sub.yj of mean value zero of the same duration and frequency as the voltage V.sub.x, but phase-displaced with respect to the latter by a quantity .phi..sub.ji. This phase displacement .phi..sub.ji makes it possible to vary the intensity of the signal to be displaced, i.e. different grey levels can be obtained.
Such a control process is described in French Pat. No. 2,279,123, filed on Feb. 6th 1974 by the present Applicant and entitled "Process for the control of an optical characteristic of a material and analog imager utilizing the process".
A binary display is obviously obtained by applying the same scanning voltages V.sub.x to rows x.sub.i and by applying to the columns y.sub.j voltages V.sub.yj of the same duration and frequency V.sub.x, either in phase or in phase opposition with respect to V.sub.x, depending on whether a white or a black is to be displayed. In both cases, it is necessary to have the same number of row control circuits as there are rows.